/*
 * opencog/atoms/reduct/FoldLink.h
 *
 * Copyright (C) 2015, 2018 Linas Vepstas
 * All Rights Reserved
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License v3 as
 * published by the Free Software Foundation and including the exceptions
 * at http://opencog.org/wiki/Licenses
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program; if not, write to:
 * Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#ifndef _OPENCOG_FOLD_LINK_H
#define _OPENCOG_FOLD_LINK_H

#include <opencog/atoms/core/FunctionLink.h>

namespace opencog
{
/** \addtogroup grp_atomspace
 *  @{
 */

/**
 * The FoldLink implements the generic reduction of lists, by
 * cons'ing together elements of the same type. See
 * http://en.wikipedia.org/wiki/Fold_(higher-order_function)
 * for a general discussion.
 */
class FoldLink : public FunctionLink
{
protected:
	Handle knil;
	virtual ValuePtr kons(AtomSpace*, bool,
	                      const ValuePtr&, const ValuePtr&) const = 0;

	void init(void);

public:
	FoldLink(const HandleSeq&&, Type);

	FoldLink(const FoldLink&) = delete;
	FoldLink& operator=(const FoldLink&) = delete;

	// Should probably be renamed to execute() ...
   virtual ValuePtr delta_reduce(AtomSpace*, bool) const;
};

LINK_PTR_DECL(FoldLink)
#define createFoldLink CREATE_DECL(FoldLink)

/** @}*/
}

#endif // _OPENCOG_FOLD_LINK_H
